CCM-14616: file scanner, update the prefix

[nhsd-angel-pastor]

Description

Code changes to integrate DL with Supplier API. Identified issues:

• variant letter was incorrect, see https://nhsd-jira.digital.nhs.uk/browse/CCM-14326
• subject from Supplier API was different than expected
  -- changed the validation of the incoming subject
  -- changed how DL builds the subject of the transitioned status
• Imported newer library from Supplier API

Context

Findings under confluence page https://nhsd-confluence.digital.nhs.uk/spaces/RIS/pages/1327224829/Digital+Letters+-+E2E+Connectivity+test+WIP

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming
• If I have used the 'skip-trivy-package' label I have done so responsibly and in the knowledge that this is being fixed as part of a separate ticket/PR.

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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.